The present invention relates to apparatus and methods for treating ischemic heart disease. In particular, the present invention relates to apparatus and methods that occlude a portion of the venous vasculature to perfuse the myocardium with blood from the venous system.
The cardiac perfusion system is composed of the left and right coronary arteries, which perfuse the myocardium from the epicardial surface to the endocardium. Blood flows through the capillaries to the coronary veins, and into the right atrium via the coronary sinus. Two additional systems, the lymphatic and the Thebesian veins, drain a portion of the blood perfused into the myocardium directly into the heart chambers. The venous system has extensive collaterals and, unlike the coronary arteries, does not occlude in atherosclerotic disease.
Atherosclerosis is a primary cause of myocardial ischemia. A number of techniques have been developed to treat atherosclerotic ischemic heart disease. These treatments have improved the lives of millions of patients worldwide, yet for certain classes of patients current technology offers little relief or hope.
Best known of the current techniques is coronary artery bypass grafting, wherein an incision is made to expose the patient""s heart, and one or more coronary arteries are replaced with saphenous veins. Conventional open heart surgery, however, is time-consuming and costly, involves a significant risk of mortality, requires a lengthy period of recuperation, and involves significant discomfort to the patient.
As a result of the foregoing drawbacks, techniques have been developed that permit coronary bypass grafting to be performed endoscopically, i.e., using elongated instruments inserted through incisions located between the ribs. A drawback of these keyhole techniques, however, is that they can be used only for coronary arteries that are readily accessible, and not, for example, those located posteriorly.
Alternatively, techniques such as percutaneous transluminal angioplasty (xe2x80x9cPTAxe2x80x9d) have been developed for reopening arteries, such as the coronary arteries, that have become constricted by plaque. In these techniques, a balloon catheter typically is inserted into the stenosis and then inflated to compress and crack the plaque lining the vessel, thereby restoring patency to the vessel. Additionally, a vascular prosthesis, commonly referred to as a xe2x80x9cstent,xe2x80x9d may be inserted transluminally and expanded within the vessel after the angioplasty procedure, to maintain the patency of the vessel after the PTA procedure.
The above-described techniques are useful only where the stenosis is localized, so that the bypass graft or PTA procedure, when completed, restores near-normal blood flow to the affected areas. For certain conditions, however, such as diffuse atherosclerosis, blockages may exist throughout much of the coronary artery system. In such situations, treatment, if possible, typically involves heart transplant.
U.S. Pat. No. 5,824,071 to Nelson et al. describes a retroperfusion technique in which one or more passageways or conduits are formed between the left ventricle and the coronary venous vasculature to supply retrograde perfusion of the myocardium. That patent discloses a valve that vents excess blood from the venous system to retain the pressure in the venous system less than a predetermined value.
Researchers also have proposed transfemoral coronary sinus balloon occlusion to treat patients with angina pectoris (Franz et al., xe2x80x9cTransfemoral Balloon Occlusion of the Coronary Sinus in Patients with Angina Pectoris,xe2x80x9d Radiologia Diagnostica, 31 (1):35-41 (1990)). Pressure-controlled intermittent coronary sinus occlusion (PICSO) is a retrograde process that intermittently occludes the coronary sinus to re-direct venous blood to the ischemic myocardium.
U.S. Pat. No. 4,934,996 to Mohl et al. describes PICSO apparatus that includes an inflatable balloon disposed on the end of a catheter, a pump and control circuitry. The distal end of the balloon catheter is inserted percutaneously or intraoperatively into the coronary sinus. The control circuitry issues a trigger signal that turns the pump on and inflates the balloon to occlude the coronary sinus. During occlusion, blood pressure in the coronary sinus increases, and blood draining into the coronary sinus through healthy heart tissue is forced back into ischemic tissue.
Mohl et al. disclose that during occlusion, pressure in the coronary sinus reaches a plateau, and that continuing to occlude the coronary sinus once the plateau is reached could damage healthy heart tissue. According, the control circuitry estimates the plateau level of the coronary sinus pressure during each occlusion, and interrupts the occlusion based on the estimate. Such previously known PICSO apparatus is cumbersome and expensive due to the complex pump and control system.
Other researchers have hypothesized that continuously partially occluding the coronary sinus may provide beneficial retroperfusion of ischemic tissue. Previously known occlusion catheters, however, have not been designed to limit venous system pressures and cost-effectively achieve this goal.
It therefore would be desirable to provide simple apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature, but without requiring an external pump and complex control circuitry.
It also would be desirable to provide apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature, but which controls pressure in the occluded vasculature so that a selected pressure parameter does not exceed a predetermined level.
It further would be desirable to provide apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature and provides an adjustable degree of occlusion, so that a selected pressure parameter does not exceed an adjustable predetermined level.
In view of the foregoing, it is an object of the present invention to provide apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature to perfuse ischemic myocardium, but without requiring an external pump and complex control circuitry.
It is another object of this invention to provide apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature, but which controls pressure in the occluded vasculature so that a selected pressure parameter does not exceed a predetermined level.
It is a further object of the present invention to provide apparatus and methods for continuously occluding all or a portion of a patient""s venous vasculature and provides an adjustable degree of occlusion, so that a selected pressure parameter does not exceed an adjustable predetermined level.
These and other objects of the invention are accomplished by providing a tubular member having an end region adapted to be disposed in a portion of a patient""s venous vasculature, e.g., the coronary sinus or great cardiac vein. The end region includes a lumen and a valve disposed proximal of the occlusion element and in communication with the lumen. An occlusion element optionally may be disposed in the end region that retains the tubular member within the patient""s venous vasculature and occludes the flow of blood around the lumen. Alternatively, the end region may be sized so that its diameter occludes the venous vasculature when urged into engagement with the walls of the lumen.
The valve controls pressure within the occluded portion of the vasculature by venting excess blood proximal of the occlusion element via the valve. The valve is preferably a slit valve, although other types of valve mechanisms, such as a duck bill valve, may be employed. Optionally, more than one valve may be provided, so that the degree of venting may be adjusted in-situ to suit a particular patient""s needs.
In a preferred embodiment, the tubular member forms an integral end of an elongated catheter adapted for percutaneous insertion. The catheter includes a proximal end that extends out of the patient""s body, and includes a hemostatic valve through which therapeutic substances, e.g., drugs or other treatment fluids, may be injected into the patient""s venous system, or through which blood may be periodically drawn, e.g., to analyze metabolites. The distal end region also may include an expandable member for regulating the pressure developed in the patient""s vasculature. As a further alternative, the tubular member may comprise a separate member which may be percutaneously deployed.
Methods of using the apparatus of the present invention to provide acute or chronic perfusion of ischemic myocardium also are provided.